Measurements of the electrical conductivity of water

The electrical conductivity of water is used in many industries as an indication of the purity of the water. A system for the traceable measurement of the conductivity of water in the range 0.01 S/m to 1 S/m is described. The method is based on the measurement of the resistance of a column of water of accurately known dimensions. There is an electrode polarisation effect and the convention is to extrapolate the conductivity as a function of inverse frequency to find the value at zero inverse frequency. The temperature coefficient of the conductivity is 2% per Kelvin at 25°C and this limits the uncertainty of the measurement to about ±0.14% of value in the present system.